This invention relates to the preparation and stabilisation of cells, and more particularly to a novel method for preparing and stabilising cells and cell suspensions, especially whole blood and constituents thereof and to the use of novel stabilised cell preparations in the quality control of analytical techniques such as UV microscopy and flow cytometric leucocyte immunophenotyping techniques, immobilised antigen/antibody detection systems and haematology analysers, and blood monitoring techniques such as zinc protoporphyrin (ZPP), red cell folate and blood glucose measurements.
UV microscopy and flow cytometry are techniques used in the diagnosis of haematological malignancies. They are also used to monitor the progress of patients infected with the Human Immunodeficiency Virus (HIV), whether asymptomatic or suffering from ARC or full-blown AIDS. Quality control (QC) of these two techniques is extremely important to arrive at the correct diagnosis and to monitor effective therapeutic regimes. The current QC methods use freshly drawn blood or microspheres coated with a fluorochrome.
The use of fresh blood on a daily basis fails to provide the information on day-to-day variation of the technique or equipment. Furthermore, fluorochrome coated microspheres, though providing a day-to-day monitor of the flow cytometer's performance, cannot be used for UV microscopy work. In addition, they cannot be used to provide quality control for the labelling techniques of leucocytes.
Fixation of normal leucocytes utilising compounds such as aldehydes, although giving stability for 5-7 days, increases cellular autofluorescence. This makes the preparation unsuitable for use as a long-term quality control material. Furthermore, the lysis of red cells by the whole blood lysing technique requires a preparation that will quality control this procedure. The current methods of fixing the leucocytes inhibit this lysing procedure, resulting in a significant increase in debris that interferes with the tests.
In International Application No. PCT/US91/03236, the entire disclosure of which is incorporated herein by reference, there is described a blood diluent and lysing agent for differential determination of white blood cells (leucocytes) in which the stabilising agent is diazolidinyl urea. Such leucocyte preparations have not been suggested as quality control preparations, possibly because they have insufficient stability and lack certain specific antigenic activity for those routine quality control procedures which need to assess results from a large number of laboratories.
International Application No. PCT/US92/03758, the entire disclosure of which is incorporated herein by reference, discloses the use of diazolidinyl urea, imidazolidinyl urea, dimethylol-5, 5-dimethylhydantion, dimethylol urea, 2-bromo-2-nitropropane-1, 3-diol and quaternary adamantane as tissue fixatives which are free of aldehydes. The formulations may inter alia contain mordants such as zinc, strontium, calcium, barium and chromium salts. It is not suggested, however, that any of these salts have stabilising properties.
Other QC equipment requiring the use of whole blood samples or blood products for calibration include haematology analysers, where currently fixed bovine blood or blood from donkeys and turkeys is used because a suitable source of stabilised human blood is not available. Zinc protoporphyrin (ZPP) and red cell folate monitoring techniques also require a fresh suspension of red blood cells for calibration, again because a suitable stabilised source is not available. Finally the lack of a stabilised source of whole human blood for calibration purposes limits the possibility for diabetics to carry out blood sugar monitoring at home.
It will be appreciated from the above that there is a need for an improved method for stabilising cells, particularly of whole blood and blood products, for a variety of quality control, monitoring and calibration applications.